Add op1_op2_relation for float operands.

Add op1_op2_relation for float operands.

op1_op2_relation can be called for relops (bool = a < b) as well as
regular binary operators (z = a + b).  This patch adds the overloaded
method for floating point results.

gcc/ChangeLog:

	* range-op-float.cc (range_operator_float::op1_op2_relation): New.
	(class foperator_equal): Add using.
	(class foperator_not_equal): Same.
	(class foperator_lt): Same.
	(class foperator_le): Same.
	(class foperator_gt): Same.
	(class foperator_ge): Same.
	* range-op.cc (range_op_handler::op1_op2_relation): New.
	* range-op.h (range_operator_float::op1_op2_relation): New.